1. Triangular movable plate articulated at posterolateral angle of abdominal somite 6 lateral to base of uropod.............. 2

– No triangular movable plate articulated at posterolateral angle of abdominal somite 6 lateral to base of uropod............ 9

2. Rostrum prominent, orbital hoods armed with teeth........................................ Alpheopsis equidactylus

– Rostrum absent, front without teeth....................................................................... 3

3. Dactyls of preopods 2–5 slender, simple.................................................................... 4

– Dactyls of pereopods 2–5 stout, bifid...................................................................... 6

4. Chela of pereopod 1 with fingers longer than palm. Large male with gaping fingers of chelipeds...... Betaeuslongidactylus

– Chela of pereopod 1 with fingers not longer than palm. Large male without gaping fingers............................ 5

5. Blade of scaphocerite broad distally. Fixed finger of pereopod 1 decreasing in width evenly to sharp curved apex................................................................................................ Betaeus harrimani

– Blade of scaphocerite narrow distally. Fixed finger of pereopod 1 truncate distal to sharp curved apex... Betaeus ensenadensis

6. Front curved, not emarginate. Symbiotic with sea urchins (Strongylocentrotus spp.)................. Betaeus macginitieae

– Front emarginate. Symbiotic with abalone or crabs or free-living................................................ 7

7. Emargination of front shallow. Telson with posterolateral spines small or missing. Symbiotic with abalones (Haliotis spp.)......................................................................................... Betaeus harfordi

– Emargination of front deep. Telson with posterolateral spines well developed. Not symbiotic with abalones.............. 8

8. Peduncle of antennule less than 0.5 carapace length. Merus of cheliped with lower inner ridge with long bristles, upper ridge ending in sharp tooth; chela 3 times as long as wide, fingers subequal to palm......................... Betaeus gracilis

– Peduncle of antennule subequal to carapace length. Merus of cheliped with lower inner ridge usually tuberculate, upper ridge with tuft of hair; chela 2 times as long as wide, fingers longer than palm.............................. Betaeus setosus

9. Eye fully exposed dorsally........................................................... Automatedolichognatha

– Eye covered by carapace............................................................................... 10

10. Pereopods without epipods. Dactyls of pereopods 3–5 bifid.................................. Synalpheus lockingtoni

– Pereopods with epipods. Dactyls of pereopods 3–5 with simple apices.......................................... 11

11. Dactyl of major chela closing horizontally. Merus of pereopod 3 with prominent inferior tooth.......... Alpheus clamator

– Dactyl of major chela closing vertically. Merus of pereopod 3 without prominent inferior tooth...................... 12

12. Orbital hoods with teeth. Minor chela with prominent tooth posterior to movable finger, movable finger flattened (lamellate)....................................................................................... Alpheusbellimanus

– Orbital hoods without teeth. Minor chela without prominent tooth posterior to movable finger, movable finger not flattened..................................................................................... Alpheus californiensis